1. Field
The present invention is in the field of processing technologies of biomass. More particularly, the invention relates to a method and equipment for fast, complete dissolution and hydrolysis of lignocellulosic biomass, and further refining biomass to value-added products.
2. Prior Art
Typical lignocellulosic biomass, such as wood and grass plants, is composed of roughly 50% cellulose, 25% hemi-cellulose, and 20% lignin. Cellulose mainly is used for producing paper. Cellulose and hemi-cellulose also can be degraded to sugars by hydrolysis for ethanol production. The existing method of dissolving lignocellulosic biomass in hot water is inefficient and incomplete. Approximately 40˜60% of woody or herbaceous biomass can be solubilized and hydrolyzed to sugars at temperatures of 200˜300° C. for 15 minutes in a batch or a semi-flow percolating reactor [Mok W S L, Antal Jr M J. Uncatalyzed solvolysis of whole biomass hemicellulose by hot compressed liquid water Ind. Eng. Chem. Res. 1992; 31:1157-1161.]. Moreover, it often results in secondary decomposition of sugars due to long reaction time and blocking flow reactors by water-insoluble residue (e.g., char). Therefore, this process needs to be cleaned periodically and cannot be operated in a continuous flow reactor at high pressures and high temperatures.
The latest research shows that hydrothermal or hot compressed water is a weakly polar solvent with acidic and basic characteristics, and it can dissolve and hydrolyze biomass. Hydrothermal water can provide homogeneous reaction conditions for biomass hydrolysis. Sasaki et al. found that a complete dissolution of cellulose was observed at 320° C. and at high water densities (>1000 kg/m3) [Sasaki m, Fang Z, Fukushima Y, Adschiri T, Arai K. Dissolution and hydrolysis of cellulose in subcritical and supercritical water Ind. & Eng. Chem. Res. 2000; 39(8):2883-2890.]. Later, Ogihara et al. studied the dissolution process over a wide range of water densities (550˜1000 kg/m3) and found that a minimum temperature of 320° C. for the complete dissolution occurred at 850 kg/m3 [Ogihara Y, Smith Jr R L, Inomata H, Arai K Direct observation of cellulose dissolution in subcritical and supercritical water over a wide range of water densities (550˜1000 kg/m3). Cellulose. 2005; 12:595-606.]. The above findings of complete solubilization are for pure cellulose. However, actual wood or grass plants contain about 50% cellulose, and the separating of pure cellulose is complicated and costly. It is difficult for the solubilization process of cellulose to be commercialized. Thus, it is necessary to find a method for complete dissolution of actual lignocellulosic biomass and for further refining to value-added products.